The present invention relates generally to maritime propulsion systems and, more particularly, to pod propulsion systems and bearing arrangements therefor.
In recent years, pod propulsion systems have gained widespread use in large vessels such as cruise ships, ferries and cargo ships. These systems can generally provide high efficiency and maneuverability with lower noise generation than traditional shaft-driven rotor systems. They also provide a high degree of layout flexibility because of the relative independence of their location relative to the primary power plant of the vessel.
Propulsion pods are relatively self-contained units that can be suspended beneath a ship's hull and independently azimuthly rotated. As shown in FIG. 1, a typical propulsion pod 10 includes one or more rotors 20 arranged within a duct or shroud 30. The rotors 20 are rotatably mounted to a shaft 40 that is centered within the duct 30 by one or more fixed support structures 50. Friction between the rotors 20 and the shaft 40 is reduced by a series of bearing assemblies 52 mounted to the support structures 50. The shaft 40 and rotors 20 may be driven by an internal electric motor or by a shaft-based drive mechanism. In some examples, the rotors 20 are surrounded by a rotating rim or drum that can be driven by a drive mechanism mounted to the housing.
Historically, the propulsion pods described above have encountered significant maintenance and reliability problems including performance degradation and outright failure of the shaft bearing system. Some of these problems are due, at least in part, to the difficulty in maintaining the correct hydrodynamic balance between the shaft, the pod housing/duct and the rotor as flow conditions and rotation speed change. The typical shaft-based pod configuration also results in inherent problems in routing and maintaining lubrication to the shaft bearing system.